docs: def _find_outOfBound(self, data, lowBound, highBound):
          """ Mask for selecting data that is out of bounds. 
          
          Parameters
          ----------
          data        : pd.DataFrame()
              Input dataframe.
          lowBound    : float
              Lower bound for dataframe.
          highBound   : float
              Higher bound for dataframe.
  
          Returns
          -------
          ???   
  
          """
  
          data = ((data < lowBound) | (data > highBound))
          return data